WASHINGTON — Federal agents are investigating allegations that the Blackwater USA security firm illegally exported dozens of firearms sound suppressors — commonly known as silencers — to Iraq and other countries for use by company operatives, sources close to the investigation tell NBC News.

Investigators from various federal agencies, including the Bureau of Alcohol, Tobacco and Firearms, Immigration and Customs Enforcement, the State Department and the Commerce Department, are digging into the allegations that the company exported the silencers without getting necessary export approval, according to law enforcement sources, who spoke to NBC News on condition of anonymity. The sources said the investigation is part of a broader examination of potential firearms and export violations.

Coincidentally, the company’s main responsibility in Iraq is protecting officials of the State Department, the agency that regulates exports of arms. The firm had more than $500 million in federal contracts in 2006.

Anne Tyrrell, a Blackwater spokeswoman, refused to comment on any specific allegations of the firearms investigation but said that “of course we would cooperate as we do in any investigation.”

The company has come under intense scrutiny since the Sept. 16 shooting deaths of 17 Iraqi civilians by Blackwater employees in an attack the Iraqi government contends was unjustified. Since then, other instances where company employees appeared to operate outside the law — including an incident in which a Blackwater employee allegedly killed a guard to Iraqi Vice President Adel Abdul Mahdi and was removed from the country with the help of the U.S. Embassy — have surfaced

The sources tell NBC News that Blackwater purchased the silencers legally from SWR Manufacturing, formerly of Georgia and now located in Pickens, S.C. SWR manufactures the devices for pistols, rifles and machine guns. The purchases took place over several years, the sources say.

Ex-official confirms Blackwater a customerA former official at SWR Manufacturing of South Carolina, also speaking on condition of anonymity, confirmed that Blackwater had been a customer. The former SWR official would not say how many suppressors Blackwater purchased, but another source said law-enforcement officials have been told that the number was more than 100.

The former SWR official said he faxed copies of all paperwork relating to Blackwater’s business with SWR to the ATF more than a year ago after federal investigators contacted him. The former official said investigators told him that Blackwater sent the silencers overseas with its employees without getting the necessary export approval.

Maarten Sengers, an expert on arms export compliance in Washington, who is not involved in the investigation, said the criminal penalties for exporting silencers without proper paperwork can be stiff — up to 10 years in prison and fines up to $1 million per count.

While silencers are rare in America because their possession is highly restricted, they are common props in movies and television programs, used by actors playing hit men or members of the special forces. The military uses them for covert action and nighttime tactical assaults where stealth and surprise are required, but experts say it is not clear why Blackwater guards would need them for missions such as personal protection of diplomats.

Details of case slow to emergeIt has been reported that two former Blackwater employees who pleaded guilty to firearms violations earlier this year are cooperating with federal investigators in a firearms investigation, but the specifics of the case, including the details about the silencers, have not previously been disclosed.

Getting permission from the State Department to export such items is extremely difficult. Several sources involved in the investigation said that in the rush to prepare for war and execute federal contracts, private security companies sometimes have overlooked the requirements for their licenses.

Controversy over Blackwater's overseas operations erupted after a major shootout in Iraq on Sept. 16 that left 17 Iraqis dead. The company claimed its guards were fired on first, but witnesses and the Iraqi government say that Blackwater operatives fired without provocation. That incident is now under FBI investigation.

The export investigation is separate from that case. A spokeswoman for the U.S. Attorney’s Office for the Eastern District of North Carolina, the district where Blackwater is based, refused to comment on the matter.